Log message:
Remove MASTER_SITES= from individual R package Makefiles.

Each R package should include ../../math/R/Makefile.extension, which also
defines MASTER_SITES.  Consequently, it is redundant for the individual
packages to do the same.  Package-specific definitions also prevent
redefining MASTER_SITES in a single common place.

Log message:
textproc/R-jsonlite: Import version 1.5

A fast JSON parser and generator optimized for statistical data and
the web. Started out as a fork of 'RJSONIO', but has been completely
rewritten in recent versions. The package offers flexible, robust,
high performance tools for working with JSON in R and is particularly
powerful for building pipelines and interacting with a web API. The
implementation is based on the mapping described in the vignette
(Ooms, 2014). In addition to converting JSON data from/to R objects,
'jsonlite' contains functions to stream, validate, and prettify JSON
data. The unit tests included with the package verify that all edge
cases are encoded and decoded consistently for use with dynamic data
in systems and applications.